The present invention relates to a device for transmitting forces in a vibration damping way, more specifically, to a coupling disc incorporated into a driveline of a motor vehicle.
As an interface system between the engine and gearbox, the coupling disc in the driveline of a motor vehicle has a major influence on the vibration behavior and thus on the acoustic behavior of the driveline of the motor vehicle. The usable speed range of an internal combustion engine contains a large number of different types of natural driveline vibrations which may be excited when the band of rotational non-uniformity of the combustion engine is passed through, thereby leading to resonances and thus noise. The tendency to use lighter and lighter engines with higher performance densities and thus with a high degree of rotational non-uniformity and lighter drivelines featuring low losses and thus fewer damping means but a higher degree of sensitivity, pushes vibration and acoustic problems more and more into the foreground and leads to more stringent requirements in respect of the interface system of the coupling disc in the driveline of the motor vehicle.
The most important tasks of the coupling disc damper are: 1) displacing the natural frequencies outside the usable speed band; 2) isolating the driveline from any excitation by the internal combustion engine; and 3) damping resonance frequencies. In principle, the coupling disc damper acts as a low pass filter.
Such a system would exhibit an ideal transmission behavior if damping were infinite in the resonance range (.omega..ltoreq..sqroot.2 .omega..sub.o) and zero in the isolation range (.omega.&gt;.sqroot.2 .omega..sub.o). The objective of all these measures is for the coupling disc to come closer to such an ideal.
The optimization of a friction disc damper is complicated by the fact that different load and operating conditions of the internal combustion engine, acceleration under full load; idling; load changes, require completely different stiffness and damping characteristics. Attempts have been made to optimize the damping behavior by using multi-step friction dampers and additional friction steps with play. Such measures complicate the systems, may lead to internal vibration and noise problems hitting the various steps and always represent a more or less unsatisfactory compromise. It becomes more and more difficult to meet the more demanding requirements by means of the conventional, friction-damped, multi-step coupling disc.
DE-AS 28 48 748 discloses a resilient coupling. The coupling has a first annular part and a second annular part. Complementary inwardly pointing surfaces at one annular part and outwardly pointing surfaces at the outer annular part form chambers and throttling channels connecting same. When one annular part rotates relative to the other annular part, the sizes of adjoining chambers change in opposite directions so that damping fluid is pressed through the channels while generating a throttling effect. On their sides, the chambers are delimited by planar radial walls.
DE 35 28 175 A1 discloses a viscous damping means on a two-part flywheel. The damping means only becomes effective after a certain freewheeling action, for example after a non-damping relative rotation of the two parts of the flywheel of .+-.10.degree.. This is ensured by uniformly circumferentially distributed damping faces on the two flywheel parts which are resiliently connected to one another, which do not overlap in an unrotated position and which, after having rotated relative to one another, form a damping gap for shearing the fluid.
DE 36 21 997 A1 discloses a two-part flywheel of the above-mentioned type where differently shaped friction linings are additionally provided across the circumference. The linings contact one another and are alternately connected to the one and the other of the flywheel parts. Initially, the damping effect is high, both in the region of the friction linings and in the region of the damping gaps, and after the two flywheel parts have rotated relative to one another, by an angle of rotation of .+-.10.degree. for example, the damping effect is clearly reduced.
A coupling disc of the species as proposed by the present invention is disclosed in U.S. Pat. No. 4,674,991 where circumferential gaps between the first annular part and the second annular part are formed by annular projections engaging one another in cross-section. The surfaces forming the circumferential gaps are provided directly at the first annular part and at the second annular part, so that the shear rate of the viscous fluid is constant as a function of the angle of rotation. The possibilities of influencing the damping characteristics are thus extremely limited.